Vanarx, also known as Yeerkbane, are long purple tube-like creatures that have a round mouth full of teeth and bodies like a raptor (dinosaur, not avian). They are native to the Yeerk homeworld, and appear to be the Yeerks' only natural predator. A Vanarx will latch itself onto the head of a Controller, then suck out and eat the Yeerk inside. Visser Three morphs a Vanarx in The Visitor as a means to eliminate useless subordinates without killing or hurting the host body.

"Where the Andalite head had been, there was now a long, thick tube. There was an opening like some horrible mouth at the end of the tube. The thing was purple, but translucent. You could almost see through it, although I wasn't sure if that was because it was a hologram, or if the animal itself was that way. The hologram Visser lowered the tube-mouth toward Chapman's head. The mouth opened, revealing hundreds, maybe thousands, of tiny suckers, each dripping slime."